Centrifugal method and means for continuously fractionating solid particles in liquid suspension thereof



May 20, 1958 F. J. FONTElN 2,835,387

CENTRIFUGAL METHOD AND MEANS FOR CONTINUOUSLY FRACTIONATING SOLID PARTICLES IN LIQUID SUPENSION THEREOF" Filed March 11. 1949 3 Sheets-Sheet 1 raw Shun-I0 FIG.1

particlu heavy Im/emor L. Freerk I Fonfein ffarnegs May 20, 1958 F. J. FONTEIN 2,835,387 CEN'IRIFUGAL METHOD AND MEANS FOR CONTINUOUSLY FRACTIONATING SOLID PARTICLES IN LIQUID SUSPENSION THEREOF Filed March 11, 1949 3 Sheets-Sheet 2 FIG-.2

Inyenfor Freerk I Fonfein 9 W, Mi 5W Af-fornegs Filed March 11, 1949 May 20, 1958 F. J. FONTEIN 2 835,387

CENTRIFUGAL METHOD AND MEANS FOR CONTINUOUSLY FRACTIONATING SOLID PARTICLES IN LIQUID SUSPENSION THEREOF 3 Sheets-Sheet 3 Invenfar Freerk I Fonf-ein B Maw,

v 'Af-farn ey s CE :1 "-W UGAL METHOD AND MEANS FOR CON- TIN UOUSLY FRACTIONATING SOLID PARTI- CLES TN LIQUID SUSPENSION THEREOF Freerk .l'. Fontein, Heerlen, Netherlands, assignor to Maatschappij voor Kolenbewerking Stamiearhon N. V.,

The invention relates to a centrifugal method and means for continuously fractionating solid particles in liquid suspension thereof.

More particularly, the invention relates to the centrifugal method, which is usually referred to as cyclonic separation, the method being performed in a cyclone separator. Such separators comprise a substantially conical separating chamber provided with a tangential infeed near the widest end thereof, a closure member with a central discharge aperture at the widest end and a second discharge aperture at the apex end of the conical separating chamber. A mass of particles in liquid suspension is introduced under fluid pressure into the separating chamber through the-tangential infeed and as a result thereof the liquid body in the tank is compelled to rapidly rotate around the axis of the tank, so that centrifugal forces are substantially in excess of gravity, the greater part of the liquid continuously discharging through the central aperture in the closure member at the widest end side of the separating chamber whereas the minor part of said liquid discharges also continuously through the second discharge aperture at the apex end of the chamber.

The rotational movement in the tank is of the returnflow type, consisting of two concentric vortices of the same rotational direction but of opposite axial direction, the outer one rotating towards the apex of the tank, the inner one rotating towards its base end. The major part of the liquid rotating in the outer vortex flows towards the axis of the tank into the inner vortex, the other part discharging through the apex aperture.

p The aparatus used in obtaining this type of fluid flow may be entirely of conical shape, but for reasons of constructional simplicity it mostly comprises a relatively short cylindrical portion, tapering into a relatively long conical portion. I

In such apparatus the denser and greater particles of a suspension of solids in a liquid medium introduced tangentially are thrown towards the circumference of the tank by the centrifugal force caused by the rotational movement, whereas the smaller ones are dragged along with the liquid into the center of the rotating liquid body and discharged therefrom through the base aperture. It may be pointed out here that the broad end side of the apparatus, near the tangential inlet may be called base, not only because it can be considered as the baseof a cone, but moreover as the rotational movement has its base at this side, the infeed of the liquid starting it along this side. Correspondingly the other side may be related to as the top side.

Various separation processes may be performed in the apparatus described hereabove. It can be used not only for dividing a mixture of particles suspended in a liquid medium into two fractions, one of which containing the coarser and/ or the denser particles and the other containing the finer and/ or lighter particles, but also to separate solids from liquid suspension in order to recover said solids or to clean the liquid medium or to obtain said suspension in a more concentrated condition. Mored States Patent F 2,835,387 Patented May 20, 1958 over, mixtures of particles of diflerent grain size and different specific gravity can be separated according to specific gravity in such apparatus by feeding the mixture in a liquid suspension medium together with a certain amount of very fine particles of a specific gravity higher than the specific gravity of separation or in a liquid suspension medium of intermediate specific gravity as is more fully described and explained in an article by Driessen, called The use of centrifugal force for cleaning fine coal in heavy liquids and suspensions with special reference to the cyclone washer published in the Journal of the Institute of Fuel, vol XIX, No. 105, December 1945, pages 33 to 44.

The control of the operation of the apparatus referred to hereabove obviously is of great importance to obtain fractions of required concentration and composition.

It is therefore an object of the invention to provide for a method and means for'controlling the concentration and composition of the separated fractions.

Moreover, it isan object of the invention to provide for a method and means for varying the concentration and composition of the fraction discharged through the apex aperture of the separator substantially without affecting the separating action in said separator.

It is still another object of the invention to provide for a method and means for eliminating screening and other like separating operations for the specific heavier fraction in the Driessen method of separation according to specific gravity as set forth; I

Also, it is an object of the invention to increase the separating effect of the cyclonic separation method and to enable a sharper separation by the method and means according to the invention.

Other objects will become apparent in the following description of the invention.

I have now found that all these objects can be obtained by the following combination of features. The discharge from the central aperture in the closure member at the widest end of the'separating chamber usually has been received in a receiving tank or overflow hood adjacent the said chamber. I now provide for outwardly directing the said discharge in a narrow thin circular stream, which in turn can be received in a receiving tank. This results in a diminution of the pressure in the core of the separating chamber, the amount of which being dependable on the resistance to the outflow of the discharge in the said annular stream. The means for obtaining such thin circular stream may be a plate close to the closure member of the separator. closure member and the plate, which hereinafter will be referred to as difiusor-rnember, may be of several appropriate designs, corresponding to the common design of cyclonic separators, I prefer a special shape of the said closure member and diifusor member as a greater sharpness of separation will be obtained in this way. This preferred closure member tapers into the separator space and at least its central part has a gradually inwardly curved shape so as to present, to the discharge, walls gradually flaring outwards. The ditlusor-plates form will be adapted to the shape of the closure member in order to obtain a' passage of equal width throughout its annular length.

I further provide for reception of the discharge from the apex end aperture of the separating chamber in a' liquid body, which is in open communication with that separating chamber. The receiving vessel being open at the top and the separating chamber being immersed at its apex end in the liquid body in said vessel, the latter and the separating chamber together constitute a set of c'om- Although the,

vessel liquid will be forced to enter the said chamber through the apex aperture thereof. So two opposite streams of liquid will pass through the apex aperture, one of which along the circumference thereof and carrying the separated fraction from the inside of the separating chamber into the receiving vessel and the. other of which returning at least part of the liquid from: the said fraction into the separating chamber, which part of the said liquid also may contain the finer and lighter particles of said fraction. In this way an additional separation is obtained, increasing the sharpness of separation of the separating chamber. Moreover the concentration of the suspension product may be increased. The discharge from the receiving vessel must be of suflrlcient capacity to pass the surplus liquid entering the said vessel.

According to a further embodiment of. this invention the pressure in the core of the separating chamber may be adjusted in such a way that the two streams of liquid compensate each other whereby the amount of liquid in the receiving vessel may be held invariable. This enables the separated solids to accumulate in the vessel,

from which they may be-removed by anysuitable means,

such as screw conveyors, elevator chains and the like. Pumping equipment for recirculating the liquid after separation of the solid-s therefrom can be eliminated in this way.

Correspondingly recirculation of the suspension ofvery fine particles of relatively high specific gravity used in the separation according to specific gravity referred to hereabove may be avoided alike as the said suspension entering the receiving chamber together with the fraction of solids of high specific gravity thereafter will be reintroduced into the separating chamber. This allows suspension of a very low density to be used as only the suspension particles leaving through the base aperture of the separator have to be supplied to the cyclone as the accumulation of suspension particles in the separator is thus increased considerably.

Another embodiment of the invention calls for the adjustment of the said core pressure at such a low value that the stream of liquid from the receiving vessel into the separating chamber will be in excess of the opposite stream and for supplying liquid from other source to said vessel to maintain the amount of liquid therein.

This enables a second additional separation to be performed by conducting the separated solids in countercurrent with the liquid supply. Separators known in the art, such as upward current classifiers, rake classifiers and the like may be used for this purpose. particles will be separated from the coarser and heavier ones and returned to the receiving vessel and therefrom to the separating chamber. The suspension of very fine particles of high specific gavity adhering to the separated solids of high specific gravity in the Driessen method of separation according to specific gravity may thus be washed from these solids and returned to the separating chamber.

The adjustment of the cores pressure can be performed in a simple way by adjusting of the distance between the closure member and the diff-uso plate. This plate therefore is provided with means for adjusting said distance, the said means being a screw spindle or the like.

The invention will be further described and explained with reference to the process for separating solids according to specific gravity as set forth and for the purpose of better understanding of its essential features only and not for limitating the scope of the invention, as it will be clear that various changes as to the construction, operation and application of the process and apparatus shown and described may be made without departingfrom the general principles.

In the accompanying drawings I have shown apparatus suitable for carrying out the invention.

Figure 1 showing diagrammatically a typicalinstalla- Fine and light tion for separating particles of different specific gravity including a cyclone in combination with an upward current classifier. Figure 2 is a diagrammatic flow sheet of a similar installation showing a cyclone in combination with a rake-classifier and 'Figure 3 is a cyclone drawn on a somewhat larger scale. In the figures like parts are indicated with like reference numerals.

Referring to Figures 1 and 2, reference numeral 1 designates a hopper containing the particles to be separated, for example, raw coal. These particles are delivered by a belt conveyor 2 to a tank 3.

Reference numeral 4 designates a hopper containing relatively fine particles of a specific gravity higher than the specific gravity of separation of the mixture to be separated. For example, these particles may be shale particles of a size below 0.2 mm. and are delivered to tank 3 by a screw conveyor 5. A pipe 6 provided with a control valve 7 supplies water to tank 3 so that a suspension is formed in which the different sized particles are kept in a substantially uniform distribution or dispersion by means of an agitator 8. This suspension is introduced by means of a pump 9 and a pipe 10 into a cyclone which is generally designated at 11.

The cyclone (see Figure 3) includes at its base end a shallow cylindrical portion 12 provided with an annular and conical base plate 13. The pipe 10 communicates tangentially with portion 12 through an opening 14. A lower conical portion 15 is connected at its upper end with the cylindrical portion by means of bolts 16, the two portions being coaxial. The apex portion 15 has an axial opening 17.

Screwed in the central opening 18 of the base plate is a vortex finder 19 having a vortex passage 20 in axial alignment with the apex opening 17 and flaring outwardly in the direction of flow.

A cyclindrical discharge hood 21 is connected by means of bolts 22 on the top of the cylindrical portion 12 and is closed by a cover plate 23 which is fixed to it by means of bolts 24. Welded on the cover plate is a nipple 25, provided with a threaded central opening 26, in which a spindle 27 can be screwed up and down by rotating the hand-wheel 28, the hand-Wheel being fixed on the spindle by means of a nut 29. The spindle protrudes through the opening 26 into the discharge hood of the cyclone. Welded to the lower end of the spindle is a diffuser plate 30 of which the surface facing the flaring vortex opening diverges in the same way as this opening.

The discharge hood is further provided with an opening 31 in the cylindrical wall from which a pipe 32 extends tangentially and is arranged to discharge onto a draining screen 33. The through-fall of this screen collects in a receiver 34 and is directed through pipe 35 to a froth flotation machine 36. This machine may be of the Kleinbentinck type and serves for removing the very fine coal particles from the suspension. The remaining suspension flows through a pipe 37 to a pump 33 from which it returns through a pipe 39 to the tank 3, to be reused as separating suspension. Obviously, fresh suspension material from hopper 4 and water from pipe 6 will only be introduced into the tank 3 to replace suspension lost in the separation circuit.

The suspension particles which are not removed from the separated fraction on the draining screen 33 are removed on a second screen 40 by spraying water through the spray-heads 41 on the separated fraction. The recovered diluted suspension is collected in a receiver 42 from Where it flows through a pipe 43 to a thickener 44. This thickener may be of the Dorr-bowl type. The thickened slurry flows through a pipe 45 to the pump 38 and is returned through pipe 39 to tank 3. The clarified liquid flows over at 46 andthrough a pipe 47 to a tank 48. This tank is provided with an adjustable weir 49. The overflowing liquid flows through pipe 50 to a pump 51 from where it is delivered through pipe 52 to the spray heads 41. If necessary the excess of liquid may be withdrawn from the system through a pipe 53 and a valve 54.

The cyclone discharges through the apex opening 17 into an open receiver 55. The receiver is at the bottom provided with a conduit 56 to which 'at the lower end liquid may be supplied from the tank 48 via a pipe 57, and a jacket 58 through the opening 59.

A screw conveyor 60 is arranged at the bottom of the conduit 56 and is adapted to discharge the separated particles at 61 at a level above the level of the liquid in the receivers 48 and 55. The conveyor is driven by an electric motor 62 via a gear transmission 63.

The suspension from the tank 3 is delivered under such a pressure by the pump 9 into the cyclone that vortices will be developed in the cyclone wherein the centrifugal force is much greater than the gravitational force acting on the particles. As a result the specifically heavy particles move into an outer stratum against the wall of the cyclone and towards and through the apex opening 17, whereas the specifically lighter particles gather in an inner stratum which ascends and discharge through the vortex passage 20 into the compartment formed by hood 21.' A great deal of the relatively fine heavy particles leave the cyclone at the apex. Due to the centrifugal force a column of air is present in the core of the cyclone of which the pressure is lower than the atmospheric pressure and which pressure may be regulated by adjusting the distance between the diffusor 30 and the base plate 13 of the cyclone.

The cyclone being provided at its apex with an open receiver 55 filled with liquid, the under pressure in the core of the cyclone can be increased by suitable adjusting the diffuser to such an extent that the liquid in the receiver rises inside the core.

By raising the level of the liquid in the receiver 55 or by increasing the suction of the cyclone a flow of liquid from the receiver 55 into the cyclone is produced which may be in excess of the flow of liquid which leaves the cyclone through the apex opening. In this way the relatively fine particles are driven back into the cyclone and a fraction which is substantially free from the fine suspension particles can be discharged from the bottom of the receiver. In the example the bottom outlet of the receiver is constructed as a hydraulic classifier by supplying liquid from tank 48 in an upward direction through the conduit 56'. In this way the relatively fine particles that might be entrained by the descending fraction will be sent back to the receiver and from there to the cyclone so that the loss of suspension material in the fraction discharged by the conveyor 60 is nil.

When using the cyclone as a classifier for fractionating solids according to their settling rate in still water the upward current classifier will cause an additional separation of the discharge from the cyclonic separator. In thickening slurries the subsequent classifier can be omitted, the receiving vessel 55 being provided with a discharge valve at or near the bottom thereof.

In the modification shown in Figure 2 the cyclone discharges with its apex in a rake-classifier 64. The clarified liquid from the thickener 44 is sent to a receiver 65. A part of the liquid is pumped from this receiver by pump 51 through pipe 52 to the spray heads 41 and another part is pumped by a pump 66 through a pipe 67 into hutch-boxes 68 where the liquid enters the inclined trough through perforations in the bottom. A reciprocating rake mechanism schematically indicated at 69 carriesthe heavy solids discharged through the apex of the cyclone step by step to the outlet 70 against the current of water 1 flowing through the hutch-boxes in the direction of the cyclone. In this way the relatively fine heavy particles are washed from the separated products and returned to the cyclone.

Reference numerals 71 and '72 indicate a bottom outlet for the receiver 65 and a discharge valve for withdrawing the excess of liquid from the circuit.

Operational instructions of this set up for a coal washery plant of 10 tons raw coal per hour calls for a cyclone having a maximum diameter of 350 mm., an apex angle of 20 degrees, inlet-, base and apex apertures of 50, 70 and 45 mm., respectively, and a feeding pressure of 1 ate. The feed consists of raw fine coal with a size up to 4 mm. in 3.5 to 4 times the amount of suspension of a specific gravity of 1.2 with which suspension a separation at a specificgravity of 1.5 can be obtained. The capacity of this cyclone is about 35 to 40 tons of water per hour. The rake classifier is of a commercially known type 200" long and 28" wide. Two tons of water per hour are introduced through the hutch boxes and this water and the discharging liquid from the apex of the cyclone are sucked up by this cyclone.

It is to be understood that the forms of my invention herewith shown and described are to be taken as examples and that various modifications may be made without departing from the spirit of the invention or the scope of the subjoined claims.

Having thus described my invention I claim:

1. The method of continuously fractionating solids in liquid suspension thereof comprising tangentially introducing under fluid pressure the suspension into a substantially conical space near the widest end thereof to move in a cyclonic vortex in said space, wherein centrifugal forces will be substantially in excess of gravity, discharging a fraction of the suspension axially at the said widest end, compelling said discharging fraction to move in an outwardly directed thin circular stream adjacent the point of discharge, discharging a second fraction of the suspension from the apex aperture of the conical space, receiving said second fraction in a liquid body in which said apex aperture is immersed, and which is in open communication with said space and at atmospheric pressure and adjusting the resistance to the discharge in said outwardly directed stream adjacent the point of discharge to change the pressure within the conical space and thereby control the flow of said liquid body entering the conical space through the apex aperture.

2. The method according to claim 1, in which the discharge from the apex end of the conical space is in excess of the'part of the liquid body entering said space through the apex end thereof, and the balance of liquid is dischargedwith fractionated solids from said liquid body.

3. The method according to claim 1, in which the dis;

charge from the apex end of the conical space balances the part of the liquid body entering said space through the apex end thereof, and the settled solids are removed from said liquid body.

4. The method according to claim 1, in which the part of the liquid body entering the conical space through the apex end thereof is in excess of the discharge from said apex end and the balance of the liquid is fed into the said liquid body.

5. The method according to claim 1, in which the part of the liquid body entering the conical space through the apex end thereof is in excess of the discharge from said apex end and the balance of the liquid is fed into the said liquid body in counter-current with the discharge of the solids from said liquid body, whereby to return part of the solids to said liquid body.

6. In apparatus for continuously fractionating solids in liquid suspension thereof a substantially conical separating chamber having a tangential inlet near the widest end thereof, a closure member with a central aperture at said end, a second aperture at the apex end of said chamber, which end is positioned in a liquid receiving vessel at a point substantially below the level of the liquid therein, the liquid in said vessel being in open communication with atmospheric air, means for outwardly directing the discharge from the said central aperture in a thin circu- 7 hr stream and means for varying the distance in axial relation between said means and said closure member.

7. Apparatus according to claim 6, in which the said means for outwardly directing thedischarge from the said central aperture comprise a difiusor-member facing the closure member of the separating chamber from the outside, the surface of which diffusor-member facing the said closure member being substantially in conformity with the outer surface of the said closure member whereby an outwardly diverging circular passage for the said discharge is created.

8. Apparatus according to claim 6, in which the said means for outwardly directing the discharge from the said central aperture comprise a diffusor-member facing the closure member of the separating chamber from the outside and enclosed in a discharge hood adjacent the separating chamber and being an integrating part thereof and supporting the means for varying the distance in axial relation between the said members.

9. Apparatus according to claim 6 in which the said closure member-tapers into the separating chamber.

10. Apparatus according to claim 6, in which at least the central part of the said closure member is curved inwardly and protruding into the separating chamber whereby to present, to the discharge, walls gradually 13. Apparatus according to claim 6, with the addition of an outlet at the bottom of the said receiving vessel.

14. Apparatus according to claim 6, with the additionof means for removing the settled solids from the said receiving vessel in counter-current with a flow of liquid.

15. Apparatus according to claim 6, with the addition of an upward current classifier directing its upward current into the receiving vessel in counter-current with the solids therefrom.

16. Apparatus according to claim 6, in which the receiving vessel forms the lower part of a rake classifier.

References Cited in the file of this patent UNITED STATES PATENTS 1,149,463 Pardee Aug. 10, 1915 1,197,946 Pardee Sept. 12, 1916 2,312,706 Freeman Mar. 2, 1943 2,377,524 Samson June 5, 1945 2,377,721 Scott June 5, 1945 2,422,203 McNeill June 17, 1947 2,533,655 Wilmot Dec. 12, 1950 2,550,340 Fontein Apr. 24, 1951 FOREIGN PATENTS 238,137 Switzerland Oct. 16, 1945 563,408 Great Britain Aug. 14,, 1944 OTHER REFERENCES Journal of the Institute of .Fuel, December 1945, The use of centrifugal force, by Driessen.

Driessen: Cleaning of coal by heavy liquids," Journal of the Institute of Fuel, August 1939, volume 12, #67, pages 335, 336 and 340. 

